The preparation of water-soluble polymers which contain sulphonic acid groups incorporated in the macromolecule has already been described in detail in numerous patents and in the technical literature. Thus, for example, the synthesis of copolymers of vinylsulphonic acid with acrylamide and vinylpyrrolidone has been published by J. Polymer Sci., 38, 147 (1959).
A process for the preparation of water-soluble copolymers of vinylsulphonic acid and acrylonitrile or methacrylonitrile, optionally in a mixture with other ethylenically unsaturated compounds, has been described in German Pat. No. 1,101,760. Copolymers of vinylsulphonates or alkylsulphonates with acrylamide and vinylamides have been described, for example, in German Auslegeschrift No. 2,444,108.
Water-soluble copolymers which contain 2-acrylamido-2-methyl-propane-3-sulphonic acid, abbreviated to AMPS in the following text, as the comonomer are described in U.S. Pat. Nos. 3,953,342 and 3,768,565, German Offenlegungsschriften Nos. 2,502,012 and 2,547,773 and U.S. Pat. Nos. 3,907,927, 3,926,718 and 3,948,783. Thus, copolymers of vinylpyrrolidone and AMPS can be prepared, for example, according to the statements of U.S. Pat. No. 3,929,741, Example 10.
However, if the copolymerization of AMPS with non-cyclic N-vinylamides of the general formula ##STR7## is carried out under analogous conditions, no polymerisation to give water-soluble products takes place.
It was thus not possible to prepare the new water-soluble copolymers according to the invention which contain both copolymerised AMPS and copolymerised non-cyclic N-vinylacylamides by the known methods.